1. Field of the Invention
The present invention relates to catheters used for surgical operations, and more specifically, to fiber optic catheters used for illuminating and ablating intravascular regions and means for guiding and positioning such catheters.
2. Description of the Related Art
Percutaneous transluminal coronary angioplasty (PTCA) is a technique for opening arterial constrictions and partial blockages called stenoses that arise from deposition of cholesterol and fibrous tissue in the walls of coronary arteries.
The human heart has three main coronary arteries which supply oxygenated blood to the heart. The opening in the aorta which marks the origin of the coronary arteries is called the ostium. In PTCA, the operator makes a puncture in an artery (usually a femoral artery in the groin) and passes a catheter up the artery past the ostium and into the coronary artery. The catheter may be a balloon catheter having at its end a balloon which, when inflated at the position of the stenosis, causes compression, stretching and splitting of the stenotic material and often expansion of the arterial wall, thereby enlarging the blood flow channel. Alternatively, the catheter may be a fiber optic catheter which uses optical fibers disposed within the catheter body to deliver energy from a source of high-intensity light (e.g., a laser) to the stenosis to ablate it. The catheter may also be of the cautery type, which uses a heated element to burn the stenosis away.
PTCA is an established technique and is used as an alternative to a bypass operation in which a section of vein, usually from the patient's leg, is used to bypass the stenosis. PTCA is performed by cardiologists and radiologists whereas by-pass surgery is carried out by cardiac surgeons. The patient in PTCA only has a local anesthetic for insertion of an introducer sheath into the femoral artery. Thereafter, a guide catheter is fed through the sheath to the ostium. The guide catheter is followed by the catheter. After successful dilatation, the patient is kept in the hospital for only one or two days and can return to work within about a week. Thus, the benefit of PTCA can be seen by contrasting it with bypass surgery which requires major surgery under full anesthesia, one or two weeks in hospital, and a substantial period of convalescence.
One type of PTCA catheter is the over-the-wire (OTW) catheter. An OTW balloon catheter has two lumens, one for inflation of the balloon at its distal end and the other for passage of a guide wire. An OTW fiber optic catheter has a coaxial lumen including an innermost lumen for the passage of a guide wire surrounded by optical fibers encapsulated by the outer lumen.
When an OTW catheter is used in PTCA, a puncture is made (again, usually in the femoral artery) and a guide catheter about 100 centimeters long is inserted into the puncture and passed into the ostium. The OTW catheter (about 135 centimeters long) is threaded over the guide wire (about 175 centimeters long) and the catheter and the guide wire are passed up the guide catheter to the ostium. Then, the guide wire is carefully slid down the coronary artery past the stenosis. The OTW catheter is slid out of the guide catheter and down the guide wire until its distal end is at the site of the stenosis. Then, in the case of a balloon OTW catheter, the balloon is inflated to dilate the artery as described above. In the case of a fiber optic catheter, the distal end of the catheter delivers light energy to the stenosis to ablate and remove it.
OTW catheters are a considerable advance over fixed wire catheters, since the guide wire can be positioned and manipulated independently to ensure that the correct artery is selected. OTW catheters also enable a doctor to monitor the position of the catheter more easily than can be done with a fixed tip design. To ensure that a fixed tip catheter is properly positioned, the doctor has to inject X-ray contrast fluid at frequent intervals. This is not obviated by the over-the-wire catheters per se, but the use of a guide wire does enable the doctor to see the wire on an X-ray fluoroscopy screen, thereby allowing him or her to control the position of the catheter.
During a PTCA procedure, it is often necessary to change OTW catheters. With conventional OTW designs, the doctor cannot withdraw the catheter while leaving the guide wire in place without significant effort. Thus, the doctor must first attach an extension to the guide wire so that the total length is about 300 centimeters. As a less preferred alternative, the guide wire can be withdrawn and substituted with one about 300 centimeters long. Thereafter, the catheter is slid off the guide wire and another catheter is substituted.
This procedure for changing catheters is cumbersome because it requires two operators to hold the guide wire, remove the first catheter and feed the replacement onto the wire. If the guide wire is removed and replaced, the patient is exposed to risk because the doctor must pass a guide wire across the stenosis for second time. It also exposes the patient to an unwanted amount of radiation, since the time required to accomplish the procedure is extended.
Some catheters have been developed which have guide wire lumens that are substantially shorter than the overall catheter body length. U.S. Pat. Nos. 5,040,548 and 5,061,273 to Yock, for example, disclose a balloon catheter having a guide wire lumen at least 10-15 centimeters long extending from the catheter's distal tip toward its proximal end. U.S. Pat. No. 4,762,129 to Bonzel discloses a similar balloon catheter where the shortened guide wire lumen is formed in the interior of and is substantially coextensive with the balloon interior. Similarly, U.S. Pat. No. 4,662,368 to Hussein et al. discloses a catheter for removing stenoses by cauterizing them with a heated tip in which the tip has a short channel for accommodating a guide wire.
U.S. Pat. No. 4,468,224 to Enzmann et al. discloses a non-PTCA catheter which, in one embodiment, uses a guide wire threading aperture set at a large angle and disposed at a moderate distance behind the catheter's distal end to introduce a guide wire into the catheter's central lumen.
It is important to note that though the above prior art catheters make use of a shortened guide wire lumen, the lumen must still be of a significant length (e.g., in the Yock device, at least 10 cm). If the guide wire lumen length is too short, the Yock patents teach that the wire cannot reliably guide the catheter to the stenosis. Instead, the flexible catheter will tend to bend and kink, thereby impeding proper positioning.